1. Field of the Invention
The present invention relates to a fixation device (fixing apparatus) to be used, for example, with an image-forming apparatus for forming an image by depositing a recording material onto a recording medium such as a paper sheet, in order to fix the recording material deposited on the recording medium.
2. Description of the Related Art
An image-forming apparatus has been hitherto known, which is provided with an image-forming means for forming an image by depositing a recording material such as toner and ink onto a recording medium such as a paper sheet and a film. Such an image-forming apparatus is provided with a fixing apparatus for fixing the recording material deposited on the recording medium by means of the image-forming means in many cases. A typical fixing apparatus comprises a fixing heating roller for heating the recording material deposited on the recording medium, and a pressing roller for pressing the recording medium against the outer circumferential surface of the fixing heating roller. The fixing apparatus constructed as described above can be operated such that the recording medium after the formation of the image is transported while being interposed by the fixing heating roller and the pressing roller to heat and pressurize the recording material together with the recording medium so that the recording material is fixed on the recording medium.
An example of the structure of the fixing heating roller is described in the section of the related art in U.S. Pat. No. 5,575,942. That is, a structure is known, in which a halogen lamp is contained at the inside, and the heat generated by the halogen lamp is conducted to the roller surface. Thus, the temperature of the entire fixing heating roller is raised. However, the halogen lamp of such a fixing heating roller is usually arranged in the vicinity of an axis of rotation of the roller. Therefore, the thermal efficiency is inferior, and a long period of time has been required to raise the temperature of the surface of the fixing heating roller to a temperature suitable for the fixing operation, from the start of electric power application to the halogen lamp.
A variety of improvements have been applied to such a fixing heating roller in order to enhance the thermal efficiency and improve the temperature-raising speed. For example, in the case of the fixing heating roller disclosed in U.S. Pat. No. 5,575,942, a resistance heat-generating member is glued and fixed on the inner circumferential surface of a main roller body which is formed to have a cylindrical configuration. The resistance heat-generating member is a heat-generating element sheet having flexibility comprising a resistance heat-generating element which is stuck to the surface of an insulative film material composed of a polyimide resin film, the resistance heat-generating element comprising a predetermined pattern of a resistance member composed of one foil film or a plurality of foil films made of stainless steel or copper. The insulative film material is formed with a conductive power supply section for applying the electric power to the resistance member. The electric power is supplied from the power supply section to the pattern of the resistance member to generate the heat. Thus, the main roller body is efficiently heated from its inner circumferential surface.
In the case of the fixing heating roller disclosed in U.S. Pat. No. 5,575,942, it is desired that a voltage such as a primary voltage, which is as high as possible, is applied to the pattern in order to further improve the temperature-raising speed. However, since the insulative film material is the flexible foil film sheet, a problem arises concerning the spatial insulation performance between the pattern of the resistance member and the main roller body. If the insulation performance is insufficient, the current flows through the main roller body, for example, via the end edge of the insulative film material, when a high voltage is applied to the pattern, which raises a possibility to cause, for example, the electric leak, the short circuit, and the dielectric breakdown. As a result, there is a possibility to cause any electric shock of a user, any generation of electric noise, and any deformation or damage of parts.
Japanese Patent Application Laid-Open No. 8-220915 discloses a fixing heating roller having a structure similar to that of the fixing heating roller disclosed in the United States Patent described above. An insulative film material, which is accommodated at the inside of a heating roller disclosed in this patent document, is arranged such that both ends in the circumferential direction are doubly overlapped in order to ensure the insulation performance between a pattern of a resistance member and a main roller body. For this reason, the thermal efficiency and the temperature-raising speed are not improved so much at the portion at which the insulative film material is doubly overlapped, as compared with other portions. Therefore, there is a possibility to cause unevenness in temperature on the outer circumferential surface of the fixing heating roller.
A first object of the present invention is to provide a fixing apparatus and an image-forming apparatus containing the same, the fixing apparatus comprising a fixing heating roller provided with a pattern of a resistance heat-generating element on a circumferential wall of a main roller body, making it possible to sufficiently ensure the insulated state of the pattern and the main roller body by means of a simple structure.
A second object of the present invention is to provide a fixing apparatus and an image-forming apparatus containing the same, the fixing apparatus comprising a pattern of a resistance heat-generating element on a circumferential wall of a main roller body, making it possible to suppress occurrence of unevenness in temperature on the outer circumference of the roller.